The present invention relates to the aggregation of asphaltenes. In particular, the present invention includes a method to determine aggregation and steps to avoid the aggregation of asphaltenes when blending petroleum oils.
Asphaltenes are a solubility class fraction of a petroleum oil or refinery process stream that typically aggregate or precipitate out of solution when concentrated, the temperature is changed, and/or when a nonpolar solvent, petroleum oil, or process stream is mixed or blended with it. Asphaltenes represent a wide variety of hydrocarbon molecules that are typically polyaromatic in nature with some degree of alkyl substitution present and which usually contain heteroatoms such as oxygen, nitrogen, and sulfur and metal atoms in their structures. Asphaltenes are usually found in significant quantities in heavy crude oils and refinery residua, and they are believed to sometimes self-assemble into colloidal micelle-like structures of several molecules that remain suspended in solution due to their small size and the possible solvating effects of other types of molecules in the petroleum oil or process stream. These micelle-like structures of several molecules are sometimes referred to as “asphaltene particles” in order to differentiate them from the single “asphaltene molecules” that may also be present in solution or suspension in the oil. The asphaltene particles are typically smaller than twenty nanometers in size, but this can vary depending upon the source of the petroleum oil or process stream and their concentration in the oil.
It is well known that insoluble asphaltenes may precipitate when two or more unprocessed petroleum crude oils and/or refinery process streams are blended together. The term “asphaltene aggregate” refers to the formation of larger precipitated clusters of asphaltene particles and molecules that stick together due to an attractive interaction that has been reinforced, when for example, the nonpolar petroleum oil and/or refinery process stream is blended into the oil containing the asphaltenes. These asphaltene aggregates are typically a micron in size and are sometimes large enough to be observed with the unaided naked eye. These aggregates are also typically physically and optically more dense than the surrounding oil mixture from which they precipitated, so they tend to slowly sediment. If the blending of such oils and/or process streams causes the aggregation or precipitation of asphaltenes, then the oils are said to be incompatible as opposed to compatible oils that do not precipitate asphaltenes on blending. Precipitated asphaltenes are not desirable, as they are known to foul and lead to fouling of process equipment when rapidly heated to high temperatures.